[Python-3000] Phasing out % string formatting

[Eric Smith]

I've proposed on another thread the no new features are added to % 
formatting, specifically the PEP 3127 (Integer Literal Support and 
Syntax) '%b' formatting.  It didn't generate any discussion, so I 
thought I'd bring it up in its own thread.

I'd like to see us take the position that % formatting is being phased 
out, if not actually starting the deprecation process.  If it's being 
phased out, then I think it makes sense to add no new features to it.

Early in the PEP 3101 (Advanced String Formatting) discussion, Guido 
said that he'd like to deprecate % formatting, but that it was too late 
in the 3.0 stage to actually do that[1] yet.  I'm not sure if the 
thinking has changed since then, but I'm hoping that it's still 
desirable to do that deprecation eventually.  And if it's going to be 
deprecated, let's not add features to it.

[1] http://mail.python.org/pipermail/python-3000/2007-August/009621.html